Background
The technical idea of communication and detection integration is originally derived from the field of radar communication integration, land combat systems are mostly provided with two electronic systems of radar and communication, and integration of the radar communication system can realize resource sharing, dynamic composition and high availability, and meanwhile, electromagnetic interference and energy consumption of the system can be reduced, maintenance cost is reduced, and comprehensive performance of the electronic systems is improved.
Similar to the case on land, underwater also faces the need for detection and communication. In recent years, the underwater operation mode gradually develops towards informatization and networking, and the existing sonar system has single function and cannot cope with more and more complex underwater conditions. The existing underwater detection and underwater acoustic communication on the platform are designed and used independently as independent devices, underwater communication and detection are often incompatible due to the existence of frequency spectrum leakage, side lobe influence, signal crosstalk, electromagnetic radiation and other effects, the sensing capability of the underwater platform is reduced due to the fact that the underwater communication and the detection cannot be carried out under the communication time slot, and the cooperation capability between the platforms is weakened due to the fact that the underwater communication and the detection cannot be carried out during detection. The traditional underwater sound detection system is greatly different from a communication system, from the function perspective, the communication system is mainly used for point-to-point data transmission, and the active sonar detection system is mainly used for judging each parameter of a target by receiving sound waves reflected by the target; from the perspective of the emission signal, the emission signal of the active sonar detection system is in a pulse form, the frequency of the signal is usually low-frequency, and the setting of the bandwidth and the pulse width is determined according to the measurement accuracy of the system on the distance and the speed; while the transmission signal of the communication system is continuous, in order to increase the communication rate, the signal frequency is usually selected to be a relatively high frequency broadband signal. From the viewpoint of performance evaluation indexes, the communication system mainly considers the problems of data transmission capacity, communication rate, confidentiality, error rate and the like, and the active sonar detection system mainly considers the maximum detection distance, speed resolution and the like.
However, the underwater acoustic communication and the underwater acoustic detection have strong similarity in the aspects of theoretical foundation, system structure, signal processing and the like, and the possibility is provided for realizing the integration of the underwater acoustic communication and the detection. And the relatively mature radar communication integrated technology on land can not be applied underwater due to the high complexity of an underwater acoustic channel. Therefore, how to combine the two technologies to realize the integration of underwater communication and detection is an important research topic in the underwater acoustic information technology.
Disclosure of Invention
The invention aims to provide an integrated underwater communication and detection method, which is an integrated method for a platform to perform underwater acoustic communication and underwater acoustic detection.
The purpose of the invention is realized as follows:
at the transmitting end:
(1.1) selecting a signal meeting the requirement as a Pattern code of the DPDS system;
(1.2) generating a large number of generalized sinusoidal frequency modulation signals which occupy the same frequency band and are close to orthogonal with each other as Pattern codes by adjusting parameters and frequency conversion reflection;
(1.3) generating transmission data;
(1.4) modulating the communication information by DPDS coding;
(1.5) transmitting after adding a synchronous signal;
at the communication receiving end:
(2.1) filtering and synchronizing the received signals first;
(2.2) performing channel equalization and Doppler compensation;
(2.3) decoding with a copy correlator;
(2.4) outputting the information sequence;
at the echo signal receiving end:
(3.1) filtering the received signal first;
(3.2) processing the filtered echo signals by adopting a multi-channel matched filter;
and (3.3) measuring the distance and speed information of the target and finishing active sonar target detection.
The invention also includes such structural features:
1. selecting signals meeting the requirements refers to: the requirement of DPDS coding communication is satisfied, and the active sonar waveform can be detected, and a large number of orthogonal waveforms occupying the same frequency band can be generated.
2. GSFM signals are selected as Pattern codes, and the function expression of the GSFM signals is as follows:
wherein: rect (t) is a rectangular function; t is the pulse width; f. of
cIs the center frequency;
is a phase modulation function, and the expression is:
where α is the modulation index, β ═ B/2 α, and B is the bandwidth of the signal; the number of cycles is expressed as C ═ α T
ρThe/, ρ are dimensionless parameters that control the shape of the instantaneous frequency function in the GSFM.
And 3, DPDS coding is to modulate the communication information in the time delay difference between adjacent Pattern codes, and simultaneously, the Pattern codes are used as pulses to carry out active sonar target detection, so that integration of underwater communication and detection is realized.
Compared with the prior art, the invention has the beneficial effects that: compared with the traditional underwater sound communication method and the active sonar detection method, the underwater sound communication method and the active sonar detection method have the difference that the purpose of communication and detection integration is achieved through the design of emission waveforms. The transmitting terminal carries communication information by using a time delay difference value between adjacent Pattern codes, and simultaneously, each Pattern code is used as an active sonar waveform to carry out target detection. That is, the present invention has the advantages that: (1) the single platform can realize the simultaneous operation of underwater acoustic communication and underwater acoustic detection; (2) compared with the traditional pulse type active sonar, the target detection refresh rate is higher; (3) the equipment can be utilized to the maximum extent; (4) the working efficiency of the sonar is effectively improved; (5) and the cooperation capability among underwater multiple platforms is improved.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
The invention comprises the following steps:
at the transmitting end:
(1) selecting a signal meeting the requirement as a Pattern code of the DPDS system;
the selected signals meeting the requirements both meet the requirements of DPDS coding communication, can be used as active sonar waveforms for detection, and can generate a large number of orthogonal waveforms occupying the same frequency band.
(2) Generating a plurality of GSFM signals which occupy the same frequency band and are close to orthogonal with each other by adjusting parameters and frequency conversion transmission;
GSFM signals are selected as Pattern codes, and the function expression of the GSFM signals is as follows:
wherein rect (t) is a rectangular function; t is the pulse width; f. of
cIs the center frequency;
is a phase modulation function, and the expression is:
where α is the modulation index, β ═ B/2 α, where B is the bandwidth of the signal; α is a frequency modulation term that determines the number of periods contained in the instantaneous frequency function of the GSFM pulse. The number of cycles can be expressed as C ═ α T
ρThe/, ρ are dimensionless parameters that control the shape of the instantaneous frequency function in the GSFM. By varying the parameters α or ρ and the frequency-converted transmission, signals occupying the same frequency band and being close to orthogonal to each other can be generated.
(3) Generating transmission data;
(4) modulating communication information through DPDS coding;
the DPDS codes modulate communication information in a time delay difference value between adjacent Pattern codes, and simultaneously, the Pattern codes are used as pulses to carry out active sonar target detection to realize integration of underwater communication and detection,
(5) transmitting after adding the synchronous signal;
at the communication receiving end:
(1) firstly, filtering and synchronizing a received signal;
(2) carrying out channel equalization and Doppler compensation;
(3) decoding by using a copy correlator;
(4) outputting the information sequence;
at the echo signal receiving end:
(1) firstly, filtering a received signal;
(2) processing the filtered echo signals by adopting a multi-channel matched filter;
(3) measuring the distance and speed information of the target, and finishing active sonar target detection;
fig. 1 is a flow chart of the underwater communication and detection integrated technology, and referring to fig. 1, the implementation steps of the invention are as follows:
the first step is as follows: and selecting a pulse signal with good autocorrelation, poor cross correlation, high speed and distance resolution and strong reverberation resistance as a Pattern code.
The correlation of the GSFM signal meets the requirement of an integrated system, and the correlation function is shown in figure 2; the GSFM signal shown in fig. 3 has a "thumbtack" -like blur function; the GSFM signal has excellent anti-reverberation performance, and as can be seen from fig. 4, under the same bandwidth and pulse width, the anti-reverberation performance of the GSFM signal is significantly better than that of the conventional CW and LFM signals. For low speed targets the GSFM signal is the best signal against reverberation in the four signals, for high speed targets the GSFM signal is slightly worse than the PN signal.
The second step is that: and determining the transmission frame structure of the integrated waveform according to the requirements of the action distance, the communication rate and the system bandwidth. Fig. 5 shows a frame structure of an integrated waveform for underwater acoustic communication sounding based on a DPDS system. T is
PThe time width of the Pattern code; t is
iThe moment when the ith code element ends; tau is
i(i ═ 1,2,3, …, L) denotes the delay value of the Pattern code in each symbol window. The integrated time domain waveform can be represented as
Wherein L is the number of different Pattern codes; p
jAnd (t) is the jth Pattern code waveform.
The third step: and generating a transmitting signal according to the waveform frame structure and the transmitting signal expression to finish the transmitting of the underwater acoustic communication and detection integrated signal.
The fourth step: and designing an underwater acoustic communication terminal receiver according to the waveform frame structure and the transmitted signal expression, and referring to fig. 6, the underwater acoustic communication terminal receiver is designed. After the received signal is filtered and synchronized, the original Pattern code is used for performing sliding correlation operation with the original Pattern code, and the pulse width T of the Pattern code is subtracted according to the difference value between the position of the correlation peak of the L-th code element Pattern code and the position of the correlation peak of the previous code element Pattern codePThe time delay value tau carried by the Lth code element can be obtainedL。
The fifth step: and designing a target echo receiver according to the waveform frame structure and the transmitted signal expression, and as shown in fig. 7, performing a detection process of the receiver. In order to avoid that the target echo cannot be received when the signal is transmitted, a transmitting-receiving split transducer is adopted, and the transmitting side and the receiving side have enough isolation. After band-pass filtering, target parameters in echo signals are measured by using a multi-channel matched filter, whether the targets exist or not is judged through threshold detection, the distance and the speed of the targets are further determined, and active sonar target detection is completed.
2. Simulation research:
simulation conditions are as follows:
the simulation scenario is shown in fig. 8, where the node a is a transceiver split system, the node a1 is an omnidirectional transmitting transducer, the node a2 is an eight-element horizontal receiving line array, and the array element spacing is 0.5 m. The node B is a six-element vertical receiving array, the array element spacing is 0.5m, and the spacing between the node A and the node B is 500 m; assume that target 1 is radially relatively stationary at a distance of 300m from node a and target 2 is radially relatively stationary at a distance of 600m from node a. At the receiving end of the node A, the echo intensity of the target 1 is 25dB, and the echo intensity of the target 2 is 16 dB. In the simulation, 20 GSFM waveforms with the pulse width T being 0.25s and orthogonal to each other are selected as Pattern codes of a DPDS system, all GSFM signals completely occupy the bandwidth (Full-Band) of the system, and the GSFM waveforms are close to orthogonal by adjusting the parameter alpha or rho and variable frequency scattering. Bandwidth of system B4 KHz, central frequency f c3 KHz. When DPDS codes, each code element carries 6bit information, the minimum coding quantization interval is 4ms, and the maximum coding time is 0.252 s. The multi-pass channel impulse response function adopted between the AB nodes in the simulation is shown in FIG. 9.
Fig. 10 is a communication simulation result, and it can be seen that the present invention has a better communication performance under the simulation condition, and the system not only has a stronger anti-noise interference capability, but also has a stable anti-multipath interference capability due to the orthogonality between different pattern codes.
Fig. 11 shows the echo signals of two targets (only the first two Pattern codes are shown). Fig. 12 and 13 show the output results of the echo signals in fig. 11 after passing through the multi-channel matched filter, and it can be seen that the target parameters obtained by processing the two echo signals are consistent with the preset parameters. Because the influence of the overlapping of the Pattern codes with excellent orthogonality on the signal processing result is small, the two Pattern codes can well complete the detection tasks of the distance and the speed of a plurality of targets.
In summary, the invention discloses an integrated underwater communication and detection method, and belongs to the technical field of underwater acoustic communication and underwater acoustic detection. The invention is realized by the following technical scheme: based on a differential Pattern delay inequality coding (DPDS) system, signals meeting requirements are selected as Pattern codes of the DPDS system, communication information is modulated in delay inequality values between adjacent Pattern codes, and each Pattern code is used as an active sonar detection waveform. And determining a decoding process of the communication detection integrated signal of the communication receiving end and a processing process of receiving the target echo by the echo signal receiving end. The communication receiving end adopts a copy correlator to obtain the time delay difference value of each code element so as to complete decoding; the integrated signal transmitting end adopts a multi-channel matched filter, measures the parameter change of echo signals, and determines the distance and the speed of a target, thereby completing active sonar target detection. The invention has the advantages that (1) the underwater acoustic communication and the underwater acoustic detection can be carried out simultaneously; (2) the equipment can be utilized to the maximum extent; (3) the working efficiency of the sonar is effectively improved; (4) and the cooperative detection among underwater multiple platforms can be carried out in real time.